1. Field of the Invention
The present invention relates to a metal cannula with a lumen (medical tube device) for insertion by percutaneous puncture to provide spinal and epidural anesthesia and pain management earlier described in Disclosure Document No. 263349 dated 20 SEP 90.
2. Description of Related Art
Spinal catheters are commonly placed intrathecally via a cannula. The cannula being introduced percutaneously and advanced to penetrate the dural membrane of the spinal column. Subsequently, a spinal catheter is introduced through the lumen of the cannula followed by removal of the cannula and indwelling retention of the catheter in the subarachnoid space. Medical and anesthetics are introduced through the indwelling catheter for effect. The indwelling catheters remain in place for extended periods to permit the injection of anesthetics or medicine as needed.
Cannula devices have been designed to minimize trauma associated with percutaneous insertion. Tip geometry has been shown to impact severity of the rent damage (cutting or tearing) to underlying vascular and neural structures and the dural membrane. Needle tip gauge has been shown to impact the size of the rent caused by the cannula. Both the size of rent AND the severity of rent are associated with complications of dural puncture: 1) vascular, neural and dural puncture membrane trauma; 2) post-dural puncture headache; 3) hematoma formation in the epidural and subarachnoid spaces; 4) paraesthesia and functional loss of nerves/neurons. Logically, pencil pointed cannula tip geometry suggests the most atraumatic design for penetration of the dural membrane fibers and avoidance of cutting of vascular and neural structures by sharp pointed cutting tip needles of the Pitkin or Quincke type (Bates, U.S. Pat. No. 4.650,472). A cannula diameter of less than 25 gauge suggests the maximal size of a sharp point beveled cannula which can penetrate the dura while maintaining a very low incidence of post dural puncture headache as opposed to traditionally large diameter needles (17 to 19 gauge) of the Hustead or Touhy tip design which are intentionally employed for administration of epidural anesthesia (Coombs, U.S. Pat. No. 4,808,157; Evans, U.S. Pat. No. 4,518,383; Cheng, U.S. Pat. No. 2,922,420).
At present, catheters specifically designed for insertion into the subarachnoid space have a diameter compatible with insertion into traditional sharp cutting tip geometry spinal cannulas (Quincke and Pitkin types) (also U.S. Pat. No. 4,994,036). These cannula are typically 25 gauge or of smaller diameter and permit introduction of a smaller diameter gauge catheter through the cannula into the subarachnoid space. Thus in order to lower the incidence of a post dural puncture headache complication associated with puncture and/or cannulation of the dural membrane, operators have traditionally employed very small diameter cannula. Small catheters are difficult to thread through the small cannula channel and accurately place in the subarachnoid space. The 32 gauge catheters currently used quickly heat to body temperature and become excessively pliable. This thwarts accurate catheter insertion and promotes knotting and kinking of the catheter in the subarachnoid space. Additionally, the small diameter of the 32 gauge catheter encourages its penetration of neural and vascular structures both upon introduction of the catheter (especially when a stylette is used to stiffen the catheter) and by migration of the indwelling catheter.
There is known a catheter set for spinal anesthesia that allows placement of a "thick spinal catheter" by threading over a guidewire previously introduced through a sharp pointed spinal needle which itself has been threaded through a sharp pointed cannula placed into the epidural space (Biscoping et al, U.S. Pat. No. 4,994,036). The main disadvantages with the invention and the process of it application are the following: 1) the sharp flat inclined tip "epidural" cannula may inadvertently puncture the dura especially since its application requires several additional manipulations associated with subarachnoid space catheter placement (threading of a spinal cannula, threading of a guidewire, threading of a catheter), and 2) accurate guidewire introduction into the subarachnoid space cannot be evaluated until the spinal cannula-guidewire assembly is removed and the cannula threaded into place. Thus the cannula could be threaded over a guidewire that was inadvertently introduced into a neural or vascular structure or even exit entirely from the subarachnoid space. This would compound the trauma to these structures and require another maneuver to attempt cannula-guidewire-catheter placement. Finally, the sharp pointed beveled tip geometry of the spinal cannula introduced through the epidural cannula acts as a cutting surface. This cutting action is traumatic to the dural membrane and underlying structures. Additionally, the cutting surface may shear either the guidewire or the spinal catheter during the application procedure.
It is known that long beveled needles used for spinal anesthesia such as the Quincke and Pitkin spinal needles can bend away from the beveled surface as the needle tip travels through the tissues. This deflection is significantly reduced if the needle possesses pencil point tip geometry.
It is also known that large gauge (22 gauge or greater diameter) spinal needles have an advantage over smaller diameter needles because a larger gauge provides better tactile and proprioceptive feedback to the operator as the needle tip is advanced through the tissues of the back during application. In addition, because the 22 gauge or larger diameter needle is more rigid, it can be more easily and accurately directed to the target site without undetected deflection of the tip.